Step 1: Divide the number into separate digits:
19817 => 1 9 8 1 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 9 = 8
9 to 8 = 1
8 to 1 = 7
1 to 7 = 6
7 to 1 = 6
Step 3: Combine the filters to a string:
8 1 7 6 6 = 81766